HAIES OF MONUTREMES AND MARSUPIALS. 573 



that between the hair and the fenestrated inner root-sheath 

 there lies a definite cuticular layer. In his discussion with regard 

 to the homology of the various parts of the hair Poulton has 

 suggested (p. 189) and has argued in favour of the theory that 

 " the hair represents the axial^ its inner root-sheath the 

 appendicular part of a feather; and thus an intelligible 

 morphological significance is given to the mysterious inner 

 root- sheath — a true part of the hair itself, and with it a rising 

 from the bulb, but which, owing to the mode of development, 

 is buried deeply beneath the surface." 



A general resume of the various theories held with regard 

 to the homologies and origin of mammalian hair has been 

 given by Benham and in the second part of this work, when 

 dealing with the development and structure of the hair in 

 Marsupials, we shall have more to say upon this point ; mean- 

 while the following will serve our present purpose. The two 

 most important views with regard to the development of the 

 various parts associated with the hair, so far as their origin 

 from the follicle is concerned, may be taken as those expressed 

 respectively by Gegenbaur and Klein. Gegenbaur ^ says 

 '' the shaft of the hair is differentiated from the invaginated 

 epidermis by cornification of its cells, while other cellular 

 parts of the follicle form the root-sheaths." Klein," on the 

 other hand, states that '^ henceforth the multiplication of the 

 cells at the bulb naturally leads to the new offspring being 

 pushed up in the axis of the hair rudiment towards the surface, 

 and becoming elongated constitute the elements of the hair 

 substance, its cuticle and inner root-sheath ; the cells of the 

 primary solid cylinder represent the rudiment of the cells of 

 the outer root-sheath only.^^ 



Schafer,^ in his figure of the longitudinal section of a hair, 

 very distinctly represents the inner root-sheath as directly 

 continuous with the outer more cornified layer of the 

 epidermis. 



' ' Comparative Anatomy,' English trans., p. 420. 



2 'Atlas of Histology,' p. 325. 



3 ' Essentials of Histology,' 1885, p. 110, fig. 133. 



